Device for the purification of exhaust gas

ABSTRACT

As a device for the purification of exhaust gas, a three-way catalyst A purifying hydrocarbon, carbon monoxide and nitrogen oxide in the vicinity of theoretical air-fuel ratio is disposed at an upstream side of the exhaust gas and an adsorption catalyst B provided with zeolite effective for the adsorption of hydrocarbon is disposed at a downstream side of the exhaust gas.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a device for the purification of an exhaustgas discharged from an internal engine for automobiles and the like.

2. Description of the Related Art

As a catalyst for the purification of an exhaust gas discharged from aninternal engine for an automobile or the like, there are widely usedcatalysts capable of simultaneously conducting oxidation of carbonmonoxide (CO) and hydrocarbon (HC) and reduction of nitrogen oxide(NOx). As disclosed in JP-B-58-20307, a greater part of these catalystsare formed by adding a noble metal such as palladium (Pd), platinum (Pt)or rhodium (Rh) as a catalyst component, and if necessary, a rare earthmetal such as cerium (Ce), lanthanum (La) or the like or an oxide of abase metal such as nickel (Ni) or the like as a co-catalyst component toan alumina coating layer formed on a refractory carrier.

Such a catalyst is strongly influenced by a temperature of the exhaustgas and an air-fuel ratio set in the engine. That is, the exhaust gastemperature for developing the purification performance by the catalystfor the automobile is generally required to be not lower than 300° C.,while the catalyst most effectively acts at the air-fuel ratio near to atheoretical air-fuel ratio (A/F=14.6) balancing the oxidation of HC andCO and the reduction of NOx. In the automobile provided with a devicefor the purification of exhaust gas using the conventional three-waycatalyst, therefore, this device is disposed at a position effectivelydeveloping the effect of the three-way catalyst and also a feedbackcontrol is carried out by detecting an oxygen concentration in theexhaust gas so as to hold the air-fuel mixture at approximatelytheoretical air-fuel ratio.

If the conventional three-way catalyst is arranged just after an exhaustmanifold, the catalyst activity is low immediately after the start ofthe engine in which the exhaust gas temperature is low (not higher than300° C.), so that there is caused a problem that a great amount of HCdischarged just after the engine start (cold start) are discharged asthey are without purification.

As the exhaust gas purifying device for solving the above problem, an HCtrapper enclosing an adsorbent for adsorbing cold HC is arranged on anupstream side of a catalyst convertor for the exhaust gas as proposed inJP-A-2-135126 and JP-A-3-141816.

In the exhaust gas purifying device disclosed in JP-A-2-135126, however,there are problems that (1) since the catalyst component is impregnatedat the downstream side of the adsorbent, HC drops off from the adsorbentbefore the catalyst reaches to its active temperature; and (2) since asolution of a catalyst metal is impregnated in zeolite, the durabilityof the catalyst component is poor. On the other hand, the exhaust gaspurifying device disclosed in JP-A-3-141816 has a problem that (3) thecontrol of dropping off the adsorbed HC is carried out by using atemperature sensor, a by-pass pipe, a control device and the like, sothat the layout of exhaust system becomes complicated and thereliability is poor and impractical.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to solve the aforementionedproblems of the conventional techniques and to provide a device for thepurification of exhaust gas which efficiently adsorbs HC of a highconcentration discharged at the start of the engine and effectivelypurify the dropped-off HC at a temperature starting the dropping of HCfrom the adsorbing layer.

The inventors have noticed the problems of the above conventionaltechniques and proposed a method of producing an adsorption catalyst, inwhich a catalyst layer is provided on a zeolite layer effective for theHC adsorption, in JP-A-7-124468 and JP-A-7-124467. In the catalystsobtained by these methods, the catalyst layer as a surface layer isheated before the inner zeolite layer, so that the catalyst layer isactivated at a stage of dropping off HC from the zeolite layer to wellpurify HC. In this connection, the inventors have further made variousstudies and confirmed that when an automobile provided at a rear surfaceof its floor with such an absorption catalyst is slowly accelerated orrun at a low speed immediately after the start of the engine, a part ofadsorbed HC drops off from the inner zeolite layer before the activationof the surface catalyst layer and hence the purification performance ofHC discharged at the engine start somewhat lowers.

In order to solve this problem, the invention provides a device for thepurification of exhaust gas in which a catalyst A obtained by coating ahoneycomb carrier with a three-way catalyst purifying HC, CO and NOx inthe vicinity of theoretical air-fuel ratio is disposed at an upstreamside of the exhaust gas and an adsorption catalyst B obtained by coatinga honeycomb carrier with zeolite effective for the adsorption ofhydrocarbon is disposed at a downstream side of the exhaust gas.

As the adsorption catalyst B, it is preferable that a catalyst layerformed by mixing powder composed mainly of activated ceria and/oralumina with at least one noble metal selected from the group consistingof platinum (Pt), palladium (Pd) and rhodium (Rh) as a catalystcomponent is provided onto zeolite layer.

The carrier used in the invention has a monolith type honeycomb shapeand includes any carriers such as cordierite, metal and the like.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described with reference to the accompanyingdrawing, wherein:

FIG. 1 is a diagrammatic view of a device for the purification ofexhaust gas used in Test Example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In general, zeolite absorbs HC at a low temperature and drops off HCwith the rise of the temperature. Although the catalyst is rapidlyactivated at a certain temperature, HC is dropped off from zeolite witha certain distribution during the rise of the temperature. In accordancewith the rise of the exhaust gas temperature, the three-way catalystarranged before the adsorption catalyst is also activated and hence thetemperature at the outlet of this catalyst or the temperature at theinlet of the adsorption catalyst is raised through reaction heat. As aresult, the surface catalyst layer in the adsorption catalyst is rapidlyactivated by the rise of the temperature, so that when the adsorbed HCis dropped off from the zeolite layer, HC is efficiently purified.Furthermore, the three-way catalyst is arranged before the adsorptioncatalyst, so that the temperature rise of the zeolite layer iscontrolled to improve the adsorption performance.

Zeolites developing sufficient HC adsorption performance over a range offrom room temperature to a relatively high temperature even in thepresence of water and having a high durability are properly selectedfrom the conventionally known zeolites as the zeolite used in theadsorption catalyst B according to the invention. For example,mordenite, USY, β-zeolite, ZSM-5 and the like are used. In order toefficiently adsorb many kinds of HC in the exhaust gas, it is preferableto mix two or more kinds of zeolites having different pore structures.

These zeolites have sufficient adsorption performance even in H-type,but the adsorption performance and the ability of preventing thedrop-off can further be improved by carrying Pd, Ag, Cu, Cr, Co, Nd orthe like on the zeolite through usual process such as ion exchangeprocess, impregnation process, immersion process or the like. Thequantity metal carried is optional, but is preferably within a range of0.1-15% by weight. When the quantity is less than 0.1% by weight, theadsorption performance and the ability of preventing the drop-off areless, while when it exceeds 15% by weight, the effect is unchangeable.

Further, the distance between the three-way catalyst A at the upstreamside and the adsorption catalyst B at the downstream side is notcritical. When the distance is too near, there is a possibility ofcausing the degradation of engine performance due to the rise of backpressure, while when it is too apart from each other, the temperature ofthe surface catalyst layer in the adsorption catalyst located at thedownstream side is not raised and there is a possibility of degradingthe purification performance of the dropped-off HC. Therefore, thedistance between the three-way catalyst A and the adsorption catalyst Bis preferably within a range of 10-50 mm.

The following examples are given in illustration of the invention andare not intended as limitations thereof. In these examples, part is byweight otherwise specified.

Example 1

Into a porcelain pot are charged 100 parts of activated ceria powdercarried with Pt (hereinafter abbreviated as Pt/CeO₂), 50 parts ofalumina and 150 parts of 2% nitric acid, which are mixed and pulverizedin an oscillation mill for 40 minutes or in a universal ball mill for6.5 hours to prepare a slurry. After a monolith cordierite carrier issubjected to a water treatment through a suction coating process, theabove slurry is applied to the whole of the carrier through wash coatingprocess and then an extra slurry is removed by the suction coatingprocess. Thereafter, the carrier is dried and calcined at 400° C. for 1hour, whereby 100 g/L of Pt/CeO₂ layer is coated onto the carrier. Thewash coating, drying and calcination are repeated to form Pt/CeO₂ layerin a total quantity of 200 g/L.

Into a porcelain pot are charged 100 parts of alumina powder carriedwith Rh (hereinafter abbreviated as Rh/Al₂O₃), 50 parts of alumina and150 parts of 2% nitric acid, which are treated in the same manner asdescribed above to prepare a slurry. The resulting slurry is appliedonto the Pt/CeO₂ layer in the same manner as described above to form 50g/L of Rh/Al₂O₃ catalyst layer, which is dried and fired in air at 650°C. for 3 hours to form a catalyst A1 for an upstream side of exhaustgas.

Separately, 100 parts of H-type ZSM-5 (SiO₂/Al₂O₃=700) (hereinafterabbreviated as ZSM-5), 215 parts of silica sol (solid content: 20%), 100parts of 10% nitric acid and 15 parts of water are charged into aporcelain pot to form a ZSM-5 slurry in the same manner as describedabove, which is applied onto a monolith carrier in a quantity of 150 g/Lin the same manner as described above, dried and fired at 400° C. for 1hour.

Onto the resulting ZSM-5 layer is applied 100 g/L of Pt/CeO₂ layer inthe same manner as described above, which is dried and fired at 400° C.for 1 hour. Further, 50 g/L of Rh/Al₂O₃ catalyst layer is applied ontothe Pt/CeO₂ layer, dried and fired in air at 650° C. for 3 hours to forman adsorption catalyst B1 for a downstream side of exhaust gas.

A tandem type adsorption catalyst-1 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB1 at the downstream side.

Example 2

Into a porcelain pot are charged 100 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 215 parts of silica sol (solid content: 20%), 100parts of 10% nitric acid and 15 parts of water to prepare ZSM-5 slurryin the same manner as in Example 1, which is applied onto a monolithcarrier in a quantity of 150 g/L in the same manner, dried and fired at400° C. for 1 hour.

Then, 100 parts of alumina powder carried with Pd (hereinafterabbreviated as Pd/Al₂O₃), 50 parts of alumina and 150 parts of 2% nitricacid are charged into a porcelain pot to prepare a slurry in the samemanner as in Example 1, which is applied onto the ZSM-5 layer as 100 g/Lof Pd/Al₂O₃ layer, dried and fired.

Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied onto thePd/Al₂O₃ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B2.

A tandem type adsorption catalyst-2 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB2 at the downstream side.

Example 3

Into a porcelain pot are charged 50 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 50 parts of H-type USY (SiO₂/Al₂O₃=50) (hereinafterabbreviated as USY), 215 parts of silica sol (solid content: 20%), 100parts of 10% nitric acid and 15 parts of water to prepare a mixed slurryof ZSM-5 and USY in the same manner as in Example 1. The mixed slurry isapplied onto a monolith carrier in a quantity of 150 g/L in the samemanner as in Example 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ layer is applied onto the mixed layer of ZSM-5and USY in the same manner as in Example 1, dried and fired.Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied onto thePt/CeO₂ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B3.

A tandem type adsorption catalyst-3 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB3 at the downstream side.

Example 4

Into a porcelain pot are charged 50 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 50 parts of H-type USY (SiO₂/Al₂O₃=50), 215 parts ofsilica sol (solid content: 20%), 100 parts of 10% nitric acid and 15parts of water to prepare a mixed slurry of ZSM-5 and USY in the samemanner as in Example 1. The mixed slurry is applied onto a monolithcarrier in a quantity of 150 g/L in the same manner as in Example 1,dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5 and USY in the same manner as in Example 2, dried and fired.Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied onto thePd/Al₂O₃ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B4.

A tandem type adsorption catalyst-4 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB4 at the downstream side.

Example 5

Into a porcelain pot are charged 67 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of H-type USY (SiO₂/Al₂O₃=50), 215 parts ofsilica sol (solid content: 20%), 100 parts of 10% nitric acid and 15parts of water to prepare a mixed slurry of ZSM-5 and USY in the samemanner as in Example 1. The mixed slurry is applied onto a monolithcarrier in a quantity of 150 g/L in the same manner as in Example 1,dried and fired.

Then, 100 g/L of Pt/CeO₂ layer is applied onto the mixed layer of ZSM-5and USY in the same manner as in Example 1, dried and fired.Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied onto thePt/CeO₂ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B5.

A tandem type adsorption catalyst-5 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB5 at the downstream side.

Example 6

Into a porcelain pot are charged 67 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of H-type USY (SiO₂/Al₂O₃=50), 215 parts ofsilica sol (solid content: 20%), 100 parts of 10% nitric acid and 15parts of water to prepare a mixed slurry of ZSM-5 and USY in the samemanner as in Example 1. The mixed slurry is applied onto a monolithcarrier in a quantity of 150 g/L in the same manner as in Example 1,dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5 and USY in the same manner as in Example 2, dried and fired.Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied onto thePd/Al₂O₃ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B6.

A tandem type adsorption catalyst-6 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB6 at the downstream side.

Example 7

Into a porcelain pot are charged 50 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 50 parts of H-type mordenite (hereinafter abbreviatedas mordenite) (SiO₂/Al₂O₃=200), 215 parts of silica sol (solid content:20%), 100 parts of 10% nitric acid and 15 parts of water to prepare amixed slurry of ZSM-5 and mordenite in the same manner as in Example 1.The mixed slurry is applied onto a monolith carrier in a quantity of 150g/L in the same manner as in Example 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ layer is applied onto the mixed layer of ZSM-5and mordenite in the same manner as in Example 1, dried and fired.Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied onto thePt/CeO₂ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B7.

A tandem type adsorption catalyst-7 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB7 at the downstream side.

Example 8

Into a porcelain pot are charged 50 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 50 parts of H-type mordenite (SiO₂/Al₂O₃=200), 215parts of silica sol (solid content: 20%), 100 parts of 10% nitric acidand 15 parts of water to prepare a mixed slurry of ZSM-5 and mordenitein the same manner as in Example 1. The mixed slurry is applied onto amonolith carrier in a quantity of 150 g/L in the same manner as inExample 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5 and mordenite in the same manner as in Example 1, dried andfired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied ontothe Pd/Al₂O₃ layer in the same manner as in Example 1, dried and firedto obtain an adsorption catalyst B8.

A tandem type adsorption catalyst-8 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB8 at the downstream side.

Example 9

Into a porcelain pot are charged 50 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 50 parts of H-type β-zeolite (hereinafter abbreviatedas β-zeolite) (SiO₂/Al₂O₃=100), 215 parts of silica sol (solid content:20%), 100 parts of 10% nitric acid and 15 parts of water to prepare amixed slurry of ZSM-5 and β-zeolite in the same manner as in Example 1.The mixed slurry is applied onto a monolith carrier in a quantity of 150g/L in the same manner as in Example 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ layer is applied onto the mixed layer of ZSM-5and β-zeolite in the same manner as in Example 1, dried and fired.Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied onto thePt/CeO₂ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B9.

A tandem type adsorption catalyst-9 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB9 at the downstream side.

Example 10

Into a porcelain pot are charged 50 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 50 parts of H-type β-zeolite (SiO₂/Al₂O₃=100), 215parts of silica sol (solid content: 20%), 100 parts of 10% nitric acidand 15 parts of water to prepare a mixed slurry of ZSM-5 and β-zeolitein the same manner as in Example 1. The mixed slurry is applied onto amonolith carrier in a quantity of 150 g/L in the same manner as inExample 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5 and β-zeolite in the same manner as in Example 2, dried andfired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied ontothe Pd/Al₂O₃ layer in the same manner as in Example 1, dried and firedto obtain an adsorption catalyst B10.

A tandem type adsorption catalyst-10 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB10 at the downstream side.

Example 11

Into a porcelain pot are charged 67 parts of H-type ZSM-5(SiO₂/Al₂₃=700), 33 parts of H-type β-zeolite (SiO₂/Al₂O₃=100), 215parts of silica sol (solid content: 20%), 100 parts of 10% nitric acidand 15 parts of water to prepare a mixed slurry of ZSM-5 and β-zeolitein the same manner as in Example 1. The mixed slurry is applied onto amonolith carrier in a quantity of 150 g/L in the same manner as inExample 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ catalyst layer is applied onto the mixed layerof ZSM-5 and β-zeolite in the same manner as in Example 1, dried andfired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied ontothe Pt/CeO₂ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B11.

A tandem type adsorption catalyst-11 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB11 at the downstream side.

Example 12

Into a porcelain pot are charged 67 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of H-type β-zeolite (SiO₂/Al₂O₃=100), 215parts of silica sol (solid content: 20%), 100 parts of 10% nitric acidand 15 parts of water to prepare a mixed slurry of ZSM-5 and β-zeolitein the same manner as in Example 1. The mixed slurry is applied onto amonolith carrier in a quantity of 150 g/L in the same manner as inExample 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5 and β-zeolite in the same manner as in Example 2, dried andfired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied ontothe Pd/Al₂O₃ layer in the same manner as in Example 1, dried and firedto obtain an adsorption catalyst B12.

A tandem type adsorption catalyst-12 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB12 at the downstream side.

Example 13

Into a porcelain pot are charged 100 parts of H-type USY(SiO₂/Al₂O₃=50), 215 parts of silica sol (solid content: 20%), 100 partsof 10% nitric acid and 15 parts of water to prepare a USY slurry in thesame manner as in Example 1. The slurry is applied onto a monolithcarrier in a quantity of 150 g/L in the same manner as in Example 1,dried and fired.

Then, 100 g/L of Pt/CeO₂ catalyst layer is applied onto the USY layer inthe same manner as in Example 1, dried and fired. Furthermore, 50 g/L ofRh/Al₂O₃ catalyst layer is applied onto the Pt/CeO₂ layer in the samemanner as in Example 1, dried and fired to obtain an adsorption catalystB13.

A tandem type adsorption catalyst-13 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB13 at the downstream side.

Example 14

Into a porcelain pot are charged 100 parts of H-type USY(SiO₂/Al₂O₃=50), 215 parts of silica sol (solid content: 20%), 100 partsof 10% nitric acid and 15 parts of water to prepare a USY slurry in thesame manner as in Example 1. The slurry is applied onto a monolithcarrier in a quantity of 150 g/L in the same manner as in Example 1,dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the USY layerin the same manner as in Example 2, dried and fired. Furthermore, 50 g/Lof Rh/Al₂O₃ catalyst layer is applied onto the Pd/Al₂O₃ layer in thesame manner as in Example 1, dried and fired to obtain an adsorptioncatalyst B14.

A tandem type adsorption catalyst-14 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB14 at the downstream side.

Example 15

Into a porcelain pot are charged 100 parts of H-type β-zeolite(SiO₂/Al₂O₃=100), 215 parts of silica sol (solid content: 20%), 100parts of 10% nitric acid and 15 parts of water to prepare a β-zeoliteslurry in the same manner as in Example 1. The slurry is applied onto amonolith carrier in a quantity of 150 g/L in the same manner as inExample 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ catalyst layer is applied onto the β-zeolitelayer in the same manner as in Example 1, dried and fired. Furthermore,50 g/L of Rh/Al₂O₃ catalyst layer is applied onto the Pt/CeO₂ layer inthe same manner as in Example 1, dried and fired to obtain an adsorptioncatalyst B15.

A tandem type adsorption catalyst-15 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB15 at the downstream side.

Example 16

Into a porcelain pot are charged 100 parts of H-type β-zeolite(SiO₂/Al₂O₃=100), 215 parts of silica sol (solid content: 20%), 100parts of 10% nitric acid and 15 parts of water to prepare a β-zeoliteslurry in the same manner as in Example 1. The slurry is applied onto amonolith carrier in a quantity of 150 g/L in the same manner as inExample 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the β-zeolitelayer in the same manner as in Example 2, dried and fired. Furthermore,50 g/L of Rh/Al₂O₃ catalyst layer is applied onto the Pd/Al₂O₃ layer inthe same manner as in Example 1, dried and fired to obtain an adsorptioncatalyst B16.

A tandem type adsorption catalyst-16 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB16 at the downstream side.

Example 17

Into a porcelain pot are charged 100 parts of H-type mordenite(SiO₂/Al₂O₃=200), 215 parts of silica sol (solid content: 20%), 100parts of 10% nitric acid and 15 parts of water to prepare a mordeniteslurry in the same manner as in Example 1. The slurry is applied onto amonolith carrier in a quantity of 150 g/L in the same manner as inExample 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ catalyst layer is applied onto the mordenitelayer in the same manner as in Example 1, dried and fired. Furthermore,50 g/L of Rh/Al₂O₃ catalyst layer is applied onto the Pt/CeO₂ layer inthe same manner as in Example 1, dried and fired to obtain an adsorptioncatalyst B17.

A tandem type adsorption catalyst-17 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB17 at the downstream side.

Example 18

Into a porcelain pot are charged 100 parts of H-type mordenite(SiO₂/Al₂O₃=200), 215 parts of silica sol (solid content: 20%), 100parts of 10% nitric acid and 15 parts of water to prepare a mordeniteslurry in the same manner as in Example 1. The slurry is applied onto amonolith carrier in a quantity of 150 g/L in the same manner as inExample 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mordenitelayer in the same manner as in Example 2, dried and fired. Furthermore,50 g/L of Rh/Al₂O₃ catalyst layer is applied onto the Pd/Al₂O₃ layer inthe same manner as in Example 1, dried and fired to obtain an adsorptioncatalyst B18.

A tandem type adsorption catalyst-18 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB18 at the downstream side.

Example 19

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of H-type USY (SiO₂/Al₂O₃=50), 33 parts ofH-type mordenite (SiO₂/Al₂O₃=200), 215 parts of silica sol (solidcontent: 20%), 100 parts of 10% nitric acid and 15 parts of water toprepare a mixed slurry of ZSM-5, USY and mordenite in the same manner asin Example 1. The mixed slurry is applied onto a monolith carrier in aquantity of 150 g/L in the same manner as in Example 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ catalyst layer is applied onto the mixed layerof ZSM-5, USY and mordenite in the same manner as in Example 1, driedand fired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is appliedonto the Pt/CeO₂ layer in the same manner as in Example 1, dried andfired to obtain an adsorption catalyst B19.

A tandem type adsorption catalyst-19 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB19 at the downstream side.

Example 20

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of H-type USY (SiO₂/Al₂₃=50), 33 parts ofH-type mordenite (SiO₂/Al₂O₃=200), 215 parts of silica sol (solidcontent: 20%), 100 parts of 10% nitric acid and 15 parts of water toprepare a mixed slurry of ZSM-5, USY and mordenite in the same manner asin Example 1. The mixed slurry is applied onto a monolith carrier in aquantity of 150 g/L in the same manner as in Example 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5, USY and mordenite in the same manner as in Example 2, driedand fired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is appliedonto the Pd/Al₂O₃ layer in the same manner as in Example 1, dried andfired to obtain an adsorption catalyst B20.

A tandem type adsorption catalyst-20 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB20 at the downstream side.

Example 21

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of H-type USY (SiO₂/Al₂O₃=50), 33 parts ofH-type β-zeolite (SiO₂/Al₂O₃=100), 215 parts of silica sol (solidcontent: 20%), 100 parts of 10% nitric acid and 15 parts of water toprepare a mixed slurry of ZSM-5, USY and β-zeolite in the same manner asin Example 1. The mixed slurry is applied onto a monolith carrier in aquantity of 150 g/L in the same manner as in Example 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ catalyst layer is applied onto the mixed layerof ZSM-5, USY and β-zeolite in the same manner as in Example 1, driedand fired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is appliedonto the Pt/CeO₂ layer in the same manner as in Example 1, dried andfired to obtain an adsorption catalyst B21.

A tandem type adsorption catalyst-21 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB21 at the downstream side.

Example 22

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of H-type USY (SiO₂/Al₂O₃=50), 33 parts ofH-type β-zeolite (SiO₂/Al₂O₃=100), 215 parts of silica sol (solidcontent: 20%), 100 parts of 10% nitric acid and 15 parts of water toprepare a mixed slurry of ZSM-5, USY and β-zeolite in the same manner asin Example 1. The mixed slurry is applied onto a monolith carrier in aquantity of 150 g/L in the same manner as in Example 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5, USY and β-zeolite in the same manner as in Example 2, driedand fired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is appliedonto the Pd/Al₂O₃ layer in the same manner as in Example 1, dried andfired to obtain an adsorption catalyst B22.

A tandem type adsorption catalyst-22 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB22 at the downstream side.

Example 23

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of Ag-ion exchanged ZSM-5 (hereinafterabbreviated as Ag-ZSM-5) (quantity of Ag carried: 5% by weight,SiO₂/Al₂O₃=30), 33 parts of H-type USY (SiO₂/Al₂O₃=50), 215 parts ofsilica sol (solid content: 20%), 100 parts of 10% nitric acid and 15parts of water to prepare a mixed slurry of ZSM-5, Ag-ZSM-5 and USY inthe same manner as in Example 1. The mixed slurry is applied onto amonolith carrier in a quantity of 150 g/L in the same manner as inExample 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ catalyst layer is applied onto the mixed layerof ZSM-5, Ag-ZSM-5 and USY in the same manner as in Example 1, dried andfired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied ontothe Pt/CeO₂ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B23.

A tandem type adsorption catalyst-23 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB23 at the downstream side.

Example 24

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂₃=700), 33 parts of Ag-ion exchanged ZSM-5 (quantity of Agcarried: 5% by weight, SiO₂/Al₂O₃=30), 33 parts of H-type USY(SiO₂/Al₂O₃=50), 215 parts of silica sol (solid content: 20%), 100 partsof 10% nitric acid and 15 parts of water to prepare a mixed slurry ofZSM-5, Ag-ZSM-5 and USY in the same manner as in Example 1. The mixedslurry is applied onto a monolith carrier in a quantity of 150 g/L inthe same manner as in Example 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5, Ag-ZSM-5 and USY in the same manner as in Example 2, dried andfired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied ontothe Pd/Al₂O₃ layer in the same manner as in Example 1, dried and firedto obtain an adsorption catalyst B24.

A tandem type adsorption catalyst-24 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB24 at the downstream side.

Example 25

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of Pd-ion exchanged ZSM-5 (hereinafterabbreviated as Pd-ZSM-5) (quantity of Pd carried: 2% by weight,SiO₂/Al₂O₃=30), 33 parts of H-type USY (SiO₂/Al₂O₃=50), 215 parts ofsilica sol (solid content: 20%), 100 parts of 10% nitric acid and 15parts of water to prepare a mixed slurry of ZSM-5, Pd-ZSM-5 and USY inthe same manner as in Example 1. The mixed slurry is applied onto amonolith carrier in a quantity of 150 g/L in the same manner as inExample 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ catalyst layer is applied onto the mixed layerof ZSM-5, Pd-ZSM-5 and USY in the same manner as in Example 1, dried andfired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied ontothe Pt/CeO₂ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B25.

A tandem type adsorption catalyst-25 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB25 at the downstream side.

Example 26

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of Pd-ion exchanged ZSM-5 (quantity of Pdcarried: 2% by weight, SiO₂/Al₂O₃=30), 33 parts of H-type USY(SiO₂/Al₂O₃=50), 215 parts of silica sol (solid content: 20%), 100 partsof 10% nitric acid and 15 parts of water to prepare a mixed slurry ofZSM-5, Pd-ZSM-5 and USY in the same manner as in Example 1. The mixedslurry is applied onto a monolith carrier in a quantity of 150 g/L inthe same manner as in Example 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5, Pd-ZSM-5 and USY in the same manner as in Example 2, dried andfired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied ontothe Pd/Al₂O₃ layer in the same manner as in Example 1, dried and firedto obtain an adsorption catalyst B26.

A tandem type adsorption catalyst-26 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB26 at the downstream side.

Example 27

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of Ag-ion exchanged ZSM-5 (quantity of Agcarried: 5% by weight, SiO₂/Al₂O₃=30), 33 parts of H-type β-zeolite(SiO₂/Al₂O₃=100), 215 parts of silica sol (solid content: 20%), 100parts of 10% nitric acid and 15 parts of water to prepare a mixed slurryof ZSM-5, Ag-ZSM-5 and β-zeolite in the same manner as in Example 1. Themixed slurry is applied onto a monolith carrier in a quantity of 150 g/Lin the same manner as in Example 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ catalyst layer is applied onto the mixed layerof ZSM-5, Ag-ZSM-5 and β-zeolite in the same manner as in Example 1,dried and fired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer isapplied onto the Pt/CeO₂ layer in the same manner as in Example 1, driedand fired to obtain an adsorption catalyst B27.

A tandem type adsorption catalyst-27 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB27 at the downstream side.

Example 28

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of Ag-ion exchanged ZSM-5 (quantity of Agcarried: 5% by weight, SiO₂/Al₂O₃=30), 33 parts of H-type β-zeolite(SiO₂/Al₂O₃=100), 215 parts of silica sol (solid content: 20%), 100parts of 10% nitric acid and 15 parts of water to prepare a mixed slurryof ZSM-5, Ag-ZSM-5 and β-zeolite in the same manner as in Example 1. Themixed slurry is applied onto a monolith carrier in a quantity of 150 g/Lin the same manner as in Example 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5, Ag-ZSM-5 and β-zeolite in the same manner as in Example 2,dried and fired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer isapplied onto the Pd/Al₂O₃ layer in the same manner as in Example 1,dried and fired to obtain an adsorption catalyst B28.

A tandem type adsorption catalyst-28 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB28 at the downstream side.

Example 29

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of Pd-ion exchanged ZSM-5 (quantity of Pdcarried: 2% by weight, SiO₂/Al₂O₃=30), 33 parts of H-type β-zeolite(SiO₂/Al₂O₃=100), 215 parts of silica sol (solid content: 20%), 100parts of 10% nitric acid and 15 parts of water to prepare a mixed slurryof ZSM-5, Pd-ZSM-5 and β-zeolite in the same manner as in Example 1. Themixed slurry is applied onto a monolith carrier in a quantity of 150 g/Lin the same manner as in Example 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ catalyst layer is applied onto the mixed layerof ZSM-5, Pd-ZSM-5 and β-zeolite in the same manner as in Example 1,dried and fired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer isapplied onto the Pt/CeO₂ layer in the same manner as in Example 1, driedand fired to obtain an adsorption catalyst B29.

A tandem type adsorption catalyst-29 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB29 at the downstream side.

Example 30

Into a porcelain pot are charged 34 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 33 parts of Pd-ion exchanged ZSM-5 (quantity of Pdcarried: 2% by weight, SiO₂/Al₂O₃=30), 33 parts of H-type β-zeolite(SiO₂/Al₂O₃=100), 215 parts of silica sol (solid content: 20%), 100parts of 10% nitric acid and 15 parts of water to prepare a mixed slurryof ZSM-5, Pd-ZSM-5 and β-zeolite in the same manner as in Example 1. Themixed slurry is applied onto a monolith carrier in a quantity of 150 g/Lin the same manner as in Example 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5, Pd-ZSM-5 and β-zeolite in the same manner as in Example 2,dried and fired. Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer isapplied onto the Pd/Al₂O₃ layer in the same manner as in Example 1,dried and fired to obtain an adsorption catalyst B30.

A tandem type adsorption catalyst-30 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB30 at the downstream side.

Example 31

Into a porcelain pot are charged 50 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 50 parts of Ag-ion exchanged USY (hereinafterabbreviated as Ag-USY) (quantity of Ag carried: 5% by weight,SiO₂/Al₂O₃=12), 215 parts of silica sol (solid content: 20%), 100 partsof 10% nitric acid and 15 parts of water to prepare a mixed slurry ofZSM-5 and Ag-USY in the same manner as in Example 1. The mixed slurry isapplied onto a monolith carrier in a quantity of 150 g/L in the samemanner as in Example 1, dried and fired.

Then, 100 g/L of Pt/CeO₂ catalyst layer is applied onto the mixed layerof ZSM-5 and Ag-USY in the same manner as in Example 1, dried and fired.Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied onto thePt/CeO₂ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B31.

A tandem type adsorption catalyst-31 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB31 at the downstream side.

Example 32

Into a porcelain pot are charged 50 parts of H-type ZSM-5(SiO₂/Al₂O₃=700), 50 parts of Ag-USY (quantity of Ag carried: 5% byweight, SiO₂/Al₂O₃=12), 215 parts of silica sol (solid content: 20%),100 parts of 10% nitric acid and 15 parts of water to prepare a mixedslurry of ZSM-5 and Ag-USY in the same manner as in Example 1. The mixedslurry is applied onto a monolith carrier in a quantity of 150 g/L inthe same manner as in Example 1, dried and fired.

Then, 100 g/L of Pd/Al₂O₃ catalyst layer is applied onto the mixed layerof ZSM-5 and Ag-USY in the same manner as in Example 2, dried and fired.Furthermore, 50 g/L of Rh/Al₂O₃ catalyst layer is applied onto thePd/Al₂O₃ layer in the same manner as in Example 1, dried and fired toobtain an adsorption catalyst B32.

A tandem type adsorption catalyst-32 is obtained by combining thethree-way catalyst A1 at the upstream side and the adsorption catalystB32 at the downstream side.

Example 33

A three-way catalyst A2 is produced in the same manner as in Example 1except that 200 g/L of Pd/CeO₂ layer is applied, dried and fired andthen 50 g/L of Rh/Al₂O₃ layer is coated on the Pd/CeO₂ layer, dried andfired in air at 650° C. for 3 hours.

A tandem type adsorption catalyst-33 is obtained by combining thethree-way catalyst A2 at the upstream side and the adsorption catalystB5 at the downstream side.

Example 34

A tandem type adsorption catalyst-34 is obtained by combining thethree-way catalyst A2 at the upstream side and the adsorption catalystB9 at the downstream side.

Comparative Example 1

Into a porcelain pot are charged 100 parts of H-type USY(SiO₂/Al₂O₃=50), 215 parts of silica sol (solid content: 20%), 100 partsof 10% nitric acid and 15 parts of water to prepare a slurry in the samemanner as in Example 1, which is applied onto a monolith carrier in aquantity of 150 g/L, dried and fired in the same manner as in Example 1to obtain an adsorption catalyst B35.

A tandem type adsorption catalyst-35 is obtained by combining theadsorption catalyst B35 at the upstream side and the three-way catalystA1 at the downstream side.

Comparative Example 2

Into a porcelain pot are charged 100 parts of H-type USY (SiO₂/Al₂O₃=7),215 parts of silica sol (solid content: 20%), 100 parts of 10% nitricacid and 15 parts of water to prepare a slurry in the same manner as inExample 1, which is applied onto a monolith carrier in a quantity of 150g/L, dried and fired in the same manner as in Example 1 to obtain anadsorption catalyst B36.

A tandem type adsorption catalyst-36 is obtained by combining theadsorption catalyst B36 at the upstream side and the three-way catalystA1 at the downstream side.

Comparative Example 3

A tandem type adsorption catalyst-37 is obtained by combining theadsorption catalyst B13 at the upstream side and the three-way catalystA1 at the downstream side.

In Table 1 are shown compositions of three-way catalyst and adsorptioncatalyst in Examples 1-34 and Comparative Examples 1-3, respectively.

TABLE 1(a) Catalyst at upstream side of exhaust gas Catalyst atdownstream side of exhaust gas Composition Quantity carried CompositionQuantity carried Example 1 inner layer Pt/CeO₂ 200 g/L inner layer ZSM5150 g/L middle layer Rh/Al₂O₃  50 g/L middle layer Pt/CeO₂ 100 g/Lsurface layer surface layer Rh/Al₂O₃  50 g/L 2 inner layer Pt/CeO₂ 200g/L inner layer ZSM5 150 g/L middle layer Rh/Al₂O₃  50 g/L middle layerPd/Al₂O₃ 100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L 3 innerlayer Pt/CeO₂ 200 g/L inner layer ZSM5:USY(1:1) 150 g/L middle layerRh/Al₂O₃  50 g/L middle layer Pt/CeO₂ 100 g/L surface layer surfacelayer Rh/Al₂O₃  50 g/L 4 inner layer Pt/CeO₂ 200 g/L inner layerZSM5:USY(1:1) 150 g/L middle layer Rh/Al₂O₃  50 g/L middle layerPd/Al₂O₃ 100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L 5 innerlayer Pt/CeO₂ 200 g/L inner layer ZSM5:USY(2:1) 150 g/L middle layerRh/Al₂O₃  50 g/L middle layer Pt/CeO₂ 100 g/L surface layer surfacelayer Rh/Al₂O₃  50 g/L 6 inner layer Pt/CeO₂ 200 g/L inner layerZSM5:USY(2:1) 150 g/L middle layer Rh/Al₂O₃  50 g/L middle layerPd/Al₂O₃ 100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L 7 innerlayer Pt/CeO₂ 200 g/L inner layer ZSM5:mordenite(1:1) 150 g/L middlelayer Rh/Al₂O₃  50 g/L middle layer Pt/CeO₂ 100 g/L surface layersurface layer Rh/Al₂O₃  50 g/L 8 inner layer Pt/CeO₂ 200 g/L inner layerZSM5:mordenite(1:1) 150 g/L middle layer Rh/Al₂O₃  50 g/L middle layerPd/Al₂O₃ 100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L 9 innerlayer Pt/CeO₂ 200 g/L inner layer ZSM5:β-zeolite(1:1) 150 g/L middlelayer Rh/Al₂O₃  50 g/L middle layer Pt/CeO₂ 100 g/L surface layersurface layer Rh/Al₂O₃  50 g/L 10  inner layer Pt/CeO₂ 200 g/L innerlayer ZSM5:β-zeolite(1:1) 150 g/L middle layer Rh/Al₂O₃  50 g/L middlelayer Pd/Al₂O₃ 100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L

TABLE 1(b) Catalyst at upstream side of exhaust gas Catalyst atdownstream side of exhaust gas Composition Quantity carried CompositionQuantity carried Example 11 inner layer Pt/CeO₂ 200 g/L inner layerZSM5:β-zeolite(2:1) 150 g/L middle layer Rh/Al₂O₃  50 g/L middle layerPt/CeO₂ 100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L 12 innerlayer Pt/CeO₂ 200 g/L inner layer ZSM5:β-zeolite(2:1) 150 g/L middlelayer Rh/Al₂O₃  50 g/L middle layer Pd/Al₂O₃ 100 g/L surface layersurface layer Rh/Al₂O₃  50 g/L 13 inner layer Pt/CeO₂ 200 g/L innerlayer USY 150 g/L middle layer Rh/Al₂O₃  50 g/L middle layer Pt/CeO₂ 100g/L surface layer surface layer Rh/Al₂O₃  50 g/L 14 inner layer Pt/CeO₂200 g/L inner layer USY 150 g/L middle layer Rh/Al₂O₃  50 g/L middlelayer Pd/Al₂O₃ 100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L 15inner layer Pt/CeO₂ 200 g/L inner layer β-zeolite 150 g/L middle layerRh/Al₂O₃  50 g/L middle layer Pt/CeO₂ 100 g/L surface layer surfacelayer Rh/Al₂O₃  50 g/L 16 inner layer Pt/CeO₂ 200 g/L inner layerβ-zeolite 150 g/L middle layer Rh/Al₂O₃  50 g/L middle layer Pd/Al₂O₃100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L 17 inner layerPt/CeO₂ 200 g/L inner layer mordenite 150 g/L middle layer Rh/Al₂O₃  50g/L middle layer Pt/CeO₂ 100 g/L surface layer surface layer Rh/Al₂O₃ 50 g/L 18 inner layer Pt/CeO₂ 200 g/L inner layer mordenite 150 g/Lmiddle layer Rh/Al₂O₃  50 g/L middle layer Pd/Al₂O₃ 100 g/L surfacelayer surface layer Rh/Al₂O₃  50 g/L 19 inner layer Pt/CeO₂ 200 g/Linner layer ZSM5:USY:mordenite(1:1:1) 150 g/L middle layer Rh/Al₂O₃  50g/L middle layer Pt/CeO₂ 100 g/L surface layer surface layer Rh/Al₂O₃ 50 g/L 20 inner layer Pt/CeO₂ 200 g/L inner layerZSM5:USY:mordenite(1:1:1) 150 g/L middle layer Rh/Al₂O₃  50 g/L middlelayer Pd/Al₂O₃ 100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L

TABLE 1(c) Catalyst at upstream side of exhaust gas Catalyst atdownstream side of exhaust gas Composition Quantity carried CompositionQuantity carried Example 21 inner layer Pt/CeO₂ 200 g/L inner layerZSM5:USY:β-zeolite(1:1:1) 150 g/L middle layer Rh/Al₂O₃  50 g/L middlelayer Pt/CeO₂ 100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L 22inner layer Pt/CeO₂ 200 g/L inner layer ZSM5:USY:β-zeolite(1:1:1) 150g/L middle layer Rh/Al₂O₃  50 g/L middle layer Pd/Al₂O₃ 100 g/L surfacelayer surface layer Rh/Al₂O₃  50 g/L 23 inner layer Pt/CeO₂ 200 g/Linner layer ZSM5:AgZSM5:USY(1:1:1) 150 g/L middle layer Rh/Al₂O₃  50 g/Lmiddle layer Pt/CeO₂ 100 g/L surface layer surface layer Rh/Al₂O₃  50g/L 24 inner layer Pt/CeO₂ 200 g/L inner layer ZSM5:AgZSM5:USY(1:1:1)150 g/L middle layer Rh/Al₂O₃  50 g/L middle layer Pd/Al₂O₃ 100 g/Lsurface layer surface layer Rh/Al₂O₃  50 g/L 25 inner layer Pt/CeO₂ 200g/L inner layer ZSM5:PdZSM5:USY(1:1:1) 150 g/L middle layer Rh/Al₂O₃  50g/L middle layer Pt/CeO₂ 100 g/L surface layer surface layer Rh/Al₂O₃ 50 g/L 26 inner layer Pt/CeO₂ 200 g/L inner layerZSM5:PdZSM5:HSY(1:1:1) 150 g/L middle layer Rh/Al₂O₃  50 g/L middlelayer Pd/Al₂O₃ 100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L 27inner layer Pt/CeO₂ 200 g/L inner layer ZSM5:AgZSM5:USY(1:1:1) 150 g/Lmiddle layer Rh/Al₂O₃  50 g/L middle layer Pt/CeO₂ 100 g/L surface layersurface layer Rh/Al₂O₃  50 g/L 28 inner layer Pt/CeO₂ 200 g/L innerlayer ZSM5:AgZSM5:β-zeolite(1:1:1) 150 g/L middle layer Rh/Al₂O₃  50 g/Lmiddle layer Pd/Al₂O₃ 100 g/L surface layer surface layer Rh/Al₂O₃  50g/L 29 inner layer Pt/CeO₂ 200 g/L inner layerZSM5:PdZSM5:β-zeolite(1:1:1) 150 g/L middle layer Rh/Al₂O₃  50 g/Lmiddle layer Pt/CeO₂ 100 g/L surface layer surface layer Rh/Al₂O₃  50g/L 30 inner layer Pt/CeO₂ 200 g/L inner layerZSM5:PdZSM5:β-zeolite(1:1:1) 150 g/L middle layer Rh/Al₂O₃  50 g/Lmiddle layer Pd/Al₂O₃ 100 g/L surface layer surface layer Rh/Al₂O₃  50g/L

TABLE 1(d) Catalyst at upstream side of exhaust gas Catalyst atdownstream side of exhaust gas Composition Quantity carried CompositionQuantity carried Example 31 inner layer Pt/CeO₂ 200 g/L inner layerZSM5:AgUSY(1:1) 150 g/L middle layer Rh/Al₂O₃  50 g/L middle layerPt/CeO₂ 100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L 32 innerlayer Pt/CeO₂ 200 g/L inner layer ZSM5:AgUSY(1:1) 150 g/L middle layerRh/Al₂O₃  50 g/L middle layer Pd/Al₂O₃ 100 g/L surface layer surfacelayer Rh/Al₂O₃  50 g/L 33 inner layer Pd/CeO₂ 200 g/L inner layerZSM5:USY(2:1) 150 g/L middle layer Rh/Al₂O₃  50 g/L middle layer Pt/CeO₂100 g/L surface layer surface layer Rh/Al₂O₃  50 g/L 34 inner layerPd/CeO₂ 200 g/L inner layer ZSM5:β-zeolite(1:1) 150 g/L middle layerRh/Al₂O₃  50 g/L middle layer Pt/CeO₂ 100 g/L surface layer surfacelayer Rh/Al₂O₃  50 g/L Compar-  1 inner layer USY(Si/2Al = 50) 150 g/Linner layer Pt/CeO₂ 200 g/L ative middle layer middle layer Rh/Al₂O₃  50g/L Example surface layer surface layer  2 inner layer USY(Si/2Al = 7)150 g/L inner layer Pt/CeO₂ 200 g/L middle layer middle layer Rh/Al₂O₃ 50 g/L surface layer surface layer  3 inner layer USY 150 g/L innerlayer Pt/CeO₂ 200 g/L middle layer Pt/CeO₂ 100 g/L middle layer Rh/Al₂O₃ 50 g/L surface layer Rh/Al₂O₃  50 g/L surface layer

Test Example

The evaluation of HC adsorption-purification performance (FTP75Abag) isconducted by using an automobile (displacement: 3000 cc, made by NissanMotor Co., Ltd.) provided with a tandem type adsorption catalystconsisting of a three-way catalyst A and an adsorption catalyst Bproduced in each of Examples 1-34 and Comparative Examples 1-3 under thefollowing evaluation conditions. The purification performance of eachadsorption catalyst B is carried out in comparison with a system havingno adsorption catalyst (provided with only the three-way catalyst A).

That is, the evaluation is as follows:

(1) An emission cut ratio is measured over a time of Abag 0-125 secondsfor evaluating an adsorption performance of HC discharged at the startof the engine.

(2) An emission cut ratio is measured over a time of Abag 0-505 secondsfor evaluating an adsorption purification performance of HC at the startof the engine and after the rise of temperature.

(i) Composition of Exhaust Gas

at engine start (0-125 seconds) aromatics 44.4% paraffin 33.3% olefin22.3% at idling of engine (125-505 seconds) aromatics 43.7% paraffin20.1% olefin 36.2%(ii) Temperature at an Inlet of Three-Way Catalyst a Located at anUpstream Side of Exhaust Gas

 0 second  25° C. 100 seconds 190° C. 200 seconds 340° C. 300 seconds470° C. 400 seconds 420° C. 500 seconds 400° C.

In the evaluation, an aged product 3 of three-way Pt—Rh catalystobtained by aging a precatalyst (0.5 L) carried with 40 g/cf of Pt/Rh atPt:Rh=5:1 at 850° C. for 100 hours (presence of combustion cut) isdisposed on an exhaust manifold 2 of an engine 1 and a B1 for thepurification of exhaust gas consisting of a three-way catalyst A (1.3 L)and an adsorption catalyst B (1.3 L) is disposed beneath a floor of theautomobile as shown in FIG. 1. The evaluation results are shown in Table2.

TABLE 2 HC cut percentage (Abag) Catalyst No. 0~125 seconds 0~505seconds Remarks Tandem type adsorption catalyst  1 47.8 10.1 Example 1 2 47.8 10.4 Example 2  3 60.3 19.2 Example 3  4 60.2 21.5 Example 4  560.7 19.5 Example 5  6 60.7 21.7 Example 6  7 50.8 17.0 Example 7  850.8 17.3 Example 8  9 60.9 21.7 Example 9 10 61.4 21.8 Example 10 1161.4 21.9 Example 11 12 48.4 22.1 Example 12 13 38.5 16.9 Example 13 1438.5 17.0 Example 14 15 54.0 19.0 Example 15 16 54.0 19.2 Example 16 1748.1 13.3 Example 17 18 48.1 13.3 Example 18 19 61.1 19.0 Example 19 2061.1 19.1 Example 20 21 61.6 22.1 Example 21 22 61.6 22.2 Example 22 2361.9 22.5 Example 23 24 61.9 22.7 Example 24 25 60.4 19.4 Example 25 2660.5 21.8 Example 26 27 62.1 22.9 Example 27 28 62.2 22.9 Example 28 2960.6 19.3 Example 29 30 60.6 19.3 Example 30 31 61.1 19.9 Example 31 3261.1 19.9 Example 32 33 60.8 20.8 Example 33 34 60.9 21.9 Example 34 3539.4 0 Comparative Example 1 36 2.0 0 Comparative Example 2 37 39.4 13.1Comparative Example 3

As mentioned above, in the exhaust gas purification device according tothe invention, the three-way catalyst obtained by coating a carrier withan inorganic material containing an active catalyst component isdisposed at an upstream side of the exhaust gas and the adsorptioncatalyst obtained by coating a zeolite adsorption layer on a carriereffective for HC adsorption with a catalyst layer is disposed at adownstream side of the exhaust gas, whereby the dropped off HC is wellpurified even at a temperature of beginning the dropping-off of HC fromthe adsorption layer.

1. A catalyst system for the purification of exhaust gases from aninternal combustion engine, consisting essentially of: (a) a catalyst Aserving for the primary purification of the exhaust gases comprising ahoneycomb carrier and a three-way catalyst formed thereon; (b) anadsorption catalyst B comprising: a honeycomb carrier; an adsorptionlayer formed thereon for the effective adsorption of hydrocarbons; and acatalyst layer comprising a noble metal selected from the groupconsisting of platinum, palladium and rhodium and at least one of ceriaand alumina, wherein the catalyst layer is a separate layer applied tothe adsorption layer and coating the adsorption layer, and wherein theadsorption catalyst B is located downstream of the catalyst A in thedirection of the exhaust gas directly; (c) means, including a directunbranched passageway between the catalyst A and the adsorption catalystB, for conducting all the exhaust gas flowing out of the catalyst A toflow into the adsorption catalyst B at all time during operation of thecatalyst system; and (d) means for supplying heat to the adsorptioncatalyst B from a heat source outside of the adsorption catalyst B,wherein the heat supplied from the heat source is supplied solely by theexhaust gases and the catalyst A.
 2. A catalyst system for thepurification of exhaust gases according to claim 1, wherein theadsorption layer includes zeolite.
 3. A catalyst system for thepurification of exhaust gases according to claim 2, wherein the zeoliteis selected from the group consisting of mordenite, USY, β-zeolite andZSM-5.
 4. A catalyst system for the purification of exhaust gasesaccording to claim 1, wherein the adsorption layer comprises a zeoliteand contains silica.
 5. A catalyst system for the purification ofexhaust gases according to claim 2, wherein the zeolite comprisesβ-zeolite and the adsorption layer contains 33 to 100% by weight ofβ-zeolite.
 6. A catalyst system for the purification of exhaust gasesaccording to claim 1, wherein the catalyst A and the adsorption catalystB are arranged in one housing together.
 7. A catalyst system for thepurification of exhaust gases according to claim 1, wherein the catalystA and the adsorption catalyst B are 10-50 mm apart.
 8. A catalyst systemfor the purification of exhaust gases according to claim 1, whichfurther consists essentially of a three-way precatalyst located upstreamof the catalyst A in the direction of the exhaust gas.
 9. A catalystsystem for the purification of exhaust gases according to claim 1,wherein the noble metal is carried on the adsorption layer in an amountof 0.1-15% by weight.
 10. A catalyst system for the purification ofexhaust gases according to claim 1, wherein the catalyst layer includesceria.
 11. A catalyst system for the purification of exhaust gasesaccording to claim 1, wherein said exhaust gas conducting meanscomprises a single pass means for conducting all the exhaust gasesflowing out of the catalyst A to flow into the adsorption catalyst Bonly a single time during operation of the catalyst system.
 12. Acatalyst system for the purification of exhaust gases according to claim1, further comprising means for transporting all exhaust gases exitingfrom the adsorption catalyst B directly to the engine exhaust dischargepipe downstream of the adsorption catalyst B.
 13. A catalyst system forthe purification of exhaust gases according to claim 1, wherein saidcatalyst A consists essentially of said honeycomb carrier and three-waycatalyst formed thereon.
 14. A catalyst system for the purification ofexhaust gases from an internal combustion engine, consisting essentiallyof: (a) a catalyst A serving for the primary purification of the exhaustgases comprising a honeycomb carrier and a three-way catalyst formedthereon; (b) an adsorption catalyst B comprising: a honeycomb carrier;an adsorption layer formed thereon for the effective adsorption ofhydrocarbons; and a catalyst layer consisting essentially of a noblemetal selected from the group consisting of platinum, palladium andrhodium, and at least one of ceria and alumina, wherein the catalystlayer is applied as a separate layer to the adsorption layer, andwherein the adsorption catalyst B is located downstream of the catalystA in the direction of the exhaust gas directly; (c) means, including adirect unbranched passageway between the catalyst A and the adsorptioncatalyst B, for conducting all the exhaust gases flowing out of thecatalyst A to flow into the adsorption catalyst B at all time duringoperation of the catalyst system; and (d) means for supplying heat tothe adsorption catalyst B from a heat source outside of the adsorptioncatalyst B, consisting essentially of engine combustion heat carried bythe exhaust gases and heat generated by reactions occurring at thecatalyst A.
 15. A catalyst system for the purification of exhaust gasesaccording to claim 14, wherein the noble metal is carried out on theadsorption layer in an amount of 0.1-15% by weight.
 16. A catalystsystem for the purification of exhaust gases according to claim 14,wherein in the adsorption catalyst B, the catalyst layer is disposed onthe adsorption layer.
 17. A catalyst system for the purification ofexhaust gases according to claim 14, wherein the adsorption layerincludes zeolite.
 18. A catalyst system for the purification of exhaustgases according to claim 17, wherein the zeolite is selected from thegroup consisting of mordenite, USY, β-zeolite and ZSM-5.
 19. A catalystsystem for the purification of exhaust gases according to claim 17,wherein the zeolite is cation exchanged with H.
 20. A catalyst systemfor the purification of exhaust gases according to claim 14, wherein theadsorption layer consists of zeolite and contains silica.
 21. A catalystsystem for the purification of exhaust gases according to claim 17,wherein the adsorption layer contains 33 to 100% by weight of β-zeolite.22. A catalyst system for the purification of exhaust gases according toclaim 14, wherein the catalyst A and the adsorption catalyst B arearranged in one housing together.
 23. A catalyst system for thepurification of exhaust gases according to claim 14, wherein thecatalyst A and the adsorption catalyst B are 10-50 mm apart.
 24. Acatalyst system for the purification of exhaust gases according to claim14, wherein the catalyst layer consists of one or more of ceria andalumina carried with the noble metal.
 25. A catalyst system for thepurification of exhaust gases according to claim 14, wherein thecatalyst layer includes ceria.
 26. A catalyst system for thepurification of exhaust gases from an internal combustion engine,consisting essentially of: (a) means for conducting exhaust gases froman internal combustion engine first into contact with a catalyst Acomprising a honeycomb carrier and a three-way catalyst formed thereon;(b) means for next causing all of the exhaust gases contacted with thecatalyst A to flow out of the catalyst A; (c) means for next causing allof the exhaust gases flowing out of the catalyst A to flow directly intoan adsorption catalyst B only a single time in a single pass system, atall time during operation of the catalyst A and the adsorption catalystB, wherein the adsorption catalyst B comprises: a honeycomb carrier; anadsorption layer formed thereon for the effective adsorption ofhydrocarbons; and a catalyst layer consisting essentially of a noblemetal selected from the group consisting of platinum, palladium andrhodium and at least one of ceria and alumina, wherein the catalystlayer is applied to the adsorption layer and is a separate layer coatingthe adsorption layer, and wherein the adsorption catalyst B is locateddownstream of the catalyst A in the direction of the exhaust gasdirectly; and (d) means for heating the adsorption catalyst B by a heatsource for supplying heat to the adsorption catalyst B from outside ofthe adsorption catalyst B, the heat source consisting essentially ofengine combustion heat carried by the exhaust gases and heat generatedby reactions occurring at the catalyst A.
 27. A catalyst system for thepurification of exhaust gases from an internal combustion engine for anautomobile, consisting essentially of: (a) means for conducting exhaustgases from an internal combustion engine first into contact with athree-way precatalyst disposed on an exhaust manifold of an engine; (b)means for conducting all of the exhaust gases contacted with thethree-way precatalyst to directly flow into a catalyst A disposedbeneath a floor of the vehicle, the catalyst A comprising a honeycombcarrier and a three-way catalyst formed thereon; (c) means for nextcausing all of the exhaust gases contacted with the catalyst A to flowout of the catalyst A; (d) means for next causing all of the exhaustgases flowing out of the catalyst A to flow directly into an adsorptioncatalyst B only a single time in a single pass system, at all timeduring operation of the catalyst A and the adsorption catalyst B,wherein the hydrocarbons are effectively adsorbed; and a catalyst layerconsisting essentially of a noble metal selected from the groupconsisting of platinum, palladium and rhodium and at least one of ceriaand alumina, wherein the adsorption catalyst B is located downstream ofthe catalyst A in the direction of the exhaust gas directly, and whereinthe adsorption catalyst B is disposed beneath the floor of the vehicle;and (e) means for heating the adsorption catalyst B by a heat source forsupplying heat to the adsorption catalyst B from outside of theadsorption catalyst B, the heat source consisting essentially of enginecombustion heat carried by the exhaust gases and heat generated byreactions occurring both at the three-way precatalyst and catalyst A.